1. Field of the Invention
The present invention relates to a hybrid drive for a non-railbound motor vehicle, which can be driven both by wheel-driving torque from an internal combustion engine and wheel-driving torque from an electric machine operated as a motor.
2. Description of the Related Art
There are different types of hybrid drives for motor vehicles. Serial hybrid drives feed the electric motor driving the driving wheels from a generator, which for its part is driven by the internal combustion engine of the motor vehicle. In this way, the internal combustion engine can be operated in a region of its characteristic map that is selected from the point of view of reducing the energy consumption and reducing pollutant emission. However, in the case of serial hybrid drives, the overall fuel consumption may be reduced only to a limited extent, and the output that is available in continuous operation is comparatively low. Under mass production boundary conditions such as cost and weight it is not possible with the current status of electric motor technology to implement driving outputs, as for example starting torque, maximum output, and maximum speed to match that of a powerful conventional drive. The advantage of serial hybrid drives is that they manage without a multi stage controlling transmission.
In the case of parallel hybrid drives, the output of the internal combustion engine and of an electric machine arranged in parallel is transmitted mechanically to the driving wheels. However, it is still necessary for a variable transmission to be arranged in the torque transmission path between the internal combustion engine and, if appropriate, the electric motor, on the one hand, and the driving wheels, on the other hand.
Furthermore, hybrid drives that can be operated in several modes of operation are known, in which the internal combustion engine and an electric machine that can be operated both as a generator and as a motor are connected to the driving wheels of the motor vehicle via a common, power-dividing transmission, for example an epicyclic transmission or a differential transmission Hybrid drives of this type manage without a variable-ratio transmission, but require either complex mechanical designs with correspondingly unfavorable efficiencies or relatively voluminous electric machines, if they are intended to produce their maximum output in continuous operation, as for example described in European Patent publication 0 744 314 A1, European Patent publication 0 743 215 A2, U.S. Pat. Nos. 5,577,973, 5,558,588, 5,558,589, 5,558,595 and in the symposium proceedings "EVS-13 The 13th International Electric Vehicle Symposium", Osaka, Japan, Vol. 1, pp. 603-610 Oct. 13-16, 1996.
It is therefore an object of the invention to provide a hybrid drive, which can be constructed in a comparatively compact form, for a motor vehicle capable of continuous operation at relatively high driving speeds.